The present disclosure provides a method of making a semiconductor material, and more particularly, the present disclosure provides a method of fabricating a strained semiconductor-on-insulator (SSOI) substrate without the need of wafer bonding.
In the semiconductor industry, there has been an increasing interest in enhancing performance of complementary metal oxide semiconductor (CMOS) devices by replacing conventional silicon-on-insulator (SOI) substrates with strained semiconductor-on-insulator (SSOI) substrates. The reason behind this interest is that SSOI substrates provide higher carrier (electrons/holes) mobility than a conventional SOI substrate. The strain in the SSOI substrates can either be compressive or tensile.
Conventional methods to fabricate SSOI substrates typically require a layer transfer process wherein a strained Si-containing layer located on a relaxed SiGe layer is transferred onto a handle wafer. In particular, the conventional process includes first creating a relaxed SiGe layer of a few microns in thickness on a surface of a Si-containing substrate. The relaxed SiGe layer typically has an in-plane lattice parameter that is larger than that of Si. Next, a Si-containing layer is grown on the relaxed SiGe layer. Because the SiGe layer has a larger in-plane lattice parameter as compared to Si, the Si-containing layer is under strain.
The structure, including the strained Si-containing layer located on a relaxed SiGe layer, is then bonded to a handle wafer, which typically includes an insulating layer, such as an oxide layer. The bonding occurs typically between the strained Si-containing layer and the insulator layer. The Si-containing substrate and the relaxed SiGe layer are then typically removed from the bonded structure to provide a strained Si-on-insulator substrate.
The conventional SSOI substrate preparation method described above is expensive and low-yielding because it combines two rather advanced substrate technologies, i.e., high-quality, thick SiGe/strain Si growth, and wafer bonding. Moreover, the conventional preparation method is unattractive for manufacturing a large volume of substrates. Also, the conventional methods of making SSOI substrates typically create a tensile strained Si-on-insulator.
In view of the above, a cost effective and manufacturable solution to fabricate SSOI substrates is still required for future high-performance semiconductor-containing CMOS products.